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  • 51. Pell, M.
    et al.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Biological Wastewater Treatment Systems2011Inngår i: Comprehensive Biotechnology, Second Edition, Elsevier, 2011, Vol. 6, s. 275-290Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Wastewater treatment (WWT) today probably is more focused on removing phosphorus and nitrogen than pathogens, since these elements contribute to eutrophication and deterioration of our natural water ecosystems. A large number of biological WWT techniques exist, from natural and constructed wetlands at one end to high-technology solutions based on the activated sludge process at the other end. The core of all WWT processes involves active microbial cells concentrated at biofilms or flocs. Knowledge of the cell and the structure and function of the microbial community is necessary in the design of effective conventional and new treatment systems. In this article, the importance of respiration, nitrogen mineralization, nitrification, denitrification, and biological phosphorus-removal processes is emphasized. Equally important is knowledge and theoretical modeling of water movement through the wastewater ecosystems. The understanding of the contact between the microbe and wastewater is a prerequisite for kinetic modeling of various enzyme reactions to describe the water purification process. Emphasis is given to the function of constructed wetlands and activated sludge processes. The future challenge of sustainable WWT is to design techniques that recycle the content of valuable plant nutrients. In addition, WWT by constructed wetlands will contribute in maintaining biological diversity in the ecosystem, as well as ideally in creating easy accessible recreational and educational meetings between urban citizens and the ecosystem.

  • 52. Petti, Olivier
    et al.
    Wang, C
    Cervantes, M
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Nilsson, H
    Numerical and experimental investigations of a hydraulic pipe during a gate closure at high Reynolds number2015Inngår i: 6th IAHR meeting of the Working Group Cavitation and dynamic problems, Faculty of technologies and systems , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The role of hydropower to provide regulated power is important to the Swedish power system. This becomes even more accentuated with the expansion of intermittent renewable electricity sources, such as wind power. The variation of hydropower operation ranges over a large spectrum of time scales, from seconds to years. For scales larger than a minute, the flow may be considered as quasi-steady from a hydrodynamic point of view. The present work addresses the shorter time scales. Such scales are manifested mainly as pressure transients, which is an issue of concern in design and operation of hydropower plants.

    The objective of the study is to address rapid pressure transients with a special focus on detailed 3D processes interacting with transients travelling in an essentially 1D geometry. The test case is a gate closing in a long rectangular pipe, where a high-Reynolds number flow is driven by a pressure difference between upper and lower water levels. Experimental time-resolved static pressure and PIV data are gathered for validation of the numerical results.

    In a first stage the computational domain is modelled in 3D with an incompressible volume of fluid method that includes the prediction of the free surfaces. The domain includes the upper and lower water tanks with free water surfaces, a pipe in-between and a closing and opening gate. The gate movement is modelled with a dynamic mesh that removes the cells as the gate closes. The block-structured mesh is generated in ICEM CFD, and parallel simulations are performed using the OpenFOAM open source software. The numerical results are compared with the experimental data, and it is shown that the experimentally observed pressure fluctuations after gate closure are not an effect of the free surfaces.

    In a second stage, the upper tank and the pipe are modelled using a compressible 1D code based on the method of characteristics (MOC). A comparison with the experimental data shows that the correct unsteady behavior of the system is captured by the 1D approach if the losses and the gate characteristics are correctly accounted for, at the same time as the compressibility is adapted to the air contents of the water and flexibility of the structure.

  • 53.
    Rehn, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Strategisk förnyelseplanering av spillvattenledningar: Med ett artificiellt neuralt nätverk som analysverktyg2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Sveriges kommunala spillvattenledningsnät står idag inför en enorm utmaning, då eftersattunderhåll i kombination med klimatförändringar kommer kräva stora framtida investeringaroch tidskrävande analyser. Detta examensarbete har utförts med målet att förenkla dettastundande förnyelsearbete. Som metod har en enkät utformats, och besvarats av totalt 84kommuner, med syftet att presentera en lägesbild. Vidare har ett artificiellt neuralt nätverkutvecklats, och tillämpats på data från Täby kommun, med syftet att förutspå vilkaspillvattenledningar i ett ledningsnät som har behov av förnyelse.

    Resultatet visar att det finns ett stort förbättringsbehov i det strategiska förnyelsearbetet.Störst behov, och potential, finns i hantering och insamling av data, där artificiella neuralanätverk kan tillämpas och utnyttjas som ett effektivt och intelligent verktyg. Det artificiellaneurala nätverket som utvecklats, och tillämpats, i detta examensarbete uppnådde en högprecision (93 %), och beräknade att Täby kommun har ca 10-20 spillvattenledningar medoupptäckt förnyelsebehov. Detta bör dock tas med viss reservation pga. bristandedatakvalitet.

    Avslutningsvis kan konstateras att lösningen för framtidens ledningsförnyelserelateradeproblem och utmaningar, ligger i förmågan att effektivt och intelligent samla in, struktureraoch analysera data om ledningsnäten. Artificiella neurala nätverk är ett verktyg som kanoch bör användas för detta ändamål då man, med hjälp av artificiell intelligens, kan göraprecisa analyser och skapa helhetsbilder över ledningsnät, vilket kan spara bådefinansiella, temporala och personella resurser.

  • 54.
    Riml, Joakim
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Solute Transport Across Scales: Time Series Analyses of Water Quality Responses to Quantify Retention and Attenuation Mechanisms in Watersheds2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The intra-continental movement of waterborne contaminants is governed by the distribution of solute load in the landscape along with the characteristics and distribution of the hydrological pathways that transport the solutes. An understanding of the processes affecting the transport and fate of the contaminants is crucial for assessments of solute concentrations and their environmental effect on downstream recipients. Elevated concentration of nutrients and the presence of anthropogenic substances, such as pharmaceutical residues, are two examples of the current problems related to hydrological transport. The overall objective of this thesis is to increase the mechanistic understanding of the governing hydrological transport processes and their links to geomorphological and biogeochemical retention and attenuation processes. Specifically, this study aims to quantify the processes governing the transport and fate of waterborne contaminants on the point, stream reach, and watershed scales by evaluating time series obtained from stream tracer tests and water quality monitoring data. The process quantification was achieved by deriving formal expressions for the key transport characteristics, such as the central temporal moments of a unit solute response function and the spectral scaling function for time series of solute responses, which attributes the solute response in the Laplace and Fourier domains to the governing processes and spatial regions within the watershed. The results demonstrate that in addition to the hydrological and biogeochemical processes, the distribution of the load in the landscape and the geomorphological properties in terms of the distribution of transport pathway distances have defined effects on the solute response. Furthermore, the spatial variability between and along the transport pathways significantly affect the solute response. The results indicate that environments with high retention and attenuation intensity, such as stream-reaches with pronounced hyporheic zones, may often dominate the solute flux in the watershed effluent, especially for reactive solutes. The mechanistic-based framework along with the evaluation methodologies presented within this study describes how the results can be generalized in terms of model parameters that reflect the hydrology, geomorphology and biogeochemistry in the studied area. This procedure is demonstrated by the parameterization of a compartment-in-series model for phosphorous transport.

  • 55.
    Riml, Joakim
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik. Swedish Meteorological and Hydrological Institute, Sweden.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Spatiotemporal decomposition of solute dispersion in watersheds2015Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, nr 4, s. 2377-2392Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Information about the effect of different dispersion mechanisms on the solute response in watersheds is crucial for understanding the temporal dynamics of many water quality problems. However, to quantify these processes from stream water quality time series may be difficult because the governing mechanisms responsible for the concentration fluctuations span a wide range of temporal and spatial scales. In an attempt to address the quantification problem, we propose a novel methodology that includes a spectral decomposition of the watershed solute response using a distributed solute transport model for the network of transport pathways in surface and subsurface water. Closed form solutions of the transport problem in both the Laplace and Fourier domains are used to derive formal expressions of (i) the central temporal moments of a solute pulse response and (ii) the power spectral response of a solute concentration time series. By evaluating high-frequency hydrochemical data from the Upper Hafren Watershed, Wales, we linked the watershed dispersion mechanisms to the damping of the concentration fluctuations in different frequency intervals reflecting various environments responsible for the damping. The evaluation of the frequency-dependent model parameters indicate that the contribution of the different environments to the concentration fluctuations at the watershed effluent varies with period. For the longest periods (predominantly groundwater transport pathways) we found that the frequency typical transport time of chloride was 100 times longer and that sodium had a 2.5 times greater retardation factor compared with the shortest periods (predominantly shallow groundwater and surface water transport pathways).

  • 56.
    Salmonsson, Alexander
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    MIKE 21 FM in Urban Flood Risk Analysis: A comparative study relating to the MIKE 21 Classic model2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Due to recent summers’ amplified frequency in intense rainstorm events, so-called cloudbursts, in places of the world not normally prone to such extreme weather phenomena, interest has aroused amongst authorities regarding measures to address in order to minimize the devastating impact of the subsequent floods. Such measures include physical planning of the townscape in terms of avoiding water to pond in inappropriate places. An important tool in this process is flood modelling. By utilizing advanced numerical hydraulic models, risk areas in the urban environment can be identified and important flow paths can be detected.

    A computer model that is able to simulate the two-dimensional surface runoff is MIKE 21, a part of the MIKE by DHI software series for water environment modelling. MIKE 21 comes in two versions, the Classic version and the Flexible Mesh (FM) version. The Classic version employs a structured orthogonal mesh to describe the topography/bathymetry of the computational domain, whilst the FM version bases its general domain description on a triangulated, unstructured mesh. In contrast to the Classic approach, the FM description allows for an altered resolution within the study area. This allows for an increase of the mesh resolution in the proximity of structures that are assumed important for the flood propagation, and a decrease in homogenous areas that are not expected to be as important regarding the general flood distribution.

    In this report, the suitability of applying the FM version in precipitation-related urban flood modelling purposes has been investigated. The results have been compared to those obtained from the Classic model, which represents the current method employed to perform these kind of analyses. The main investigations have been conducted in scenarios representing a rainfall event with a return period of 100 years. As no calibration data was available for the sites investigated at this kind of extreme event, the results only relate to each other.

    The results showed no significant difference between the models regarding where water generally will flow and accumulate. However, the spatial and volumetric distribution of the water in risk areas is more severe in the Classic model’s results. This was assessed to be the consequence of a parameter, only existing in the FM model, which suppresses the momentum equations of the model and by doing so, retains water in the mesh elements and prevents it to flow unimpeded until a certain depth is achieved. Too low values of this parameter caused instabilities in the program. Additionally, the required workload to set up the FM model was found significantly higher compared to the Classic model. Accordingly, no sensible reason to change from the Classic to the FM approach in urban flood modelling could be found.

  • 57. Schmadel, Noah M.
    et al.
    Neilson, Bethany T.
    Heavilin, Justin E.
    Stevens, David K.
    Worman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    The influence of spatially variable stream hydraulics on reach scale transient storage modeling2014Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, nr 12, s. 9287-9299Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Within the context of reach scale transient storage modeling, there is limited understanding of how best to establish reach segment lengths that represent the effects of spatially variable hydraulic and geomorphic channel properties. In this paper, we progress this understanding through the use of channel property distributions derived from high-resolution imagery that are fundamental for hydraulic routing. We vary the resolution of reach segments used in the model representation and investigate the minimum number necessary to capture spatially variable influences on downstream predictions of solute residence time probability density functions while sufficiently representing the observed channel property distributions. We also test if the corresponding statistical moments of the predictions provide comparable results and, therefore, a method for establishing appropriate reach segment lengths. We find that the predictions and the moment estimates begin to represent the majority of the variability at reach segment lengths coinciding with distances where observed channel properties are spatially correlated. With this approach, reach scales where the channel properties no longer significantly change predictions can be established, which provides a foundation for more focused transient storage modeling efforts.

  • 58. Schmadel, Noah M.
    et al.
    Neilson, Bethany T.
    Heavilin, Justin E.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Isolating parameter sensitivity in reach scale transient storage modeling2016Inngår i: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 89, s. 24-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Parameter sensitivity analyses, although necessary to assess identifiability, may not lead to an increased understanding or accurate representation of transient storage processes when associated parameter sensitivities are muted. Reducing the number of uncertain calibration parameters through field-based measurements may allow for more realistic representations and improved predictive capabilities of reach scale stream solute transport. Using a two-zone transient storage model, we examined the spatial detail necessary to set parameters describing hydraulic characteristics and isolate the sensitivity of the parameters associated with transient storage processes. We represented uncertain parameter distributions as triangular fuzzy numbers and used closed form statistical moment solutions to express parameter sensitivity thus avoiding copious model simulations. These solutions also allowed for the direct incorporation of different levels of spatial information regarding hydraulic characteristics. To establish a baseline for comparison, we performed a sensitivity analysis considering all model parameters as uncertain. Next, we set hydraulic parameters as the reach averages, leaving the transient storage parameters as uncertain, and repeated the analysis. Lastly, we incorporated high resolution hydraulic information assessed from aerial imagery to examine whether more spatial detail was necessary to isolate the sensitivity of transient storage parameters. We found that a reach-average hydraulic representation, as opposed to using detailed spatial information, was sufficient to highlight transient storage parameter sensitivity and provide more information regarding the potential identifiability of these parameters.

  • 59.
    Sondal, Jannike
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Att förenkla hydraulisk modellering vid översvämningskartering - Betydelsen av tvärsektionernas geometri under vattenytan vid normala flöden2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Idag ses information om tvärsektionens geometri under vattenytan som vital för att kunna utföra översvämningskarteringar. Att ta fram sådan information kan dock många gånger vara en både tids- och resurskrävande process, varför det är intressant att undersöka möjligheterna av att förenkla denna del av översvämningskarteringen. Med Väsbyån som studieområde syftade denna studie därför till att undersöka hur viktig tvärsektionens geometri under vattenytan är, i förhållande till Mannings tal, för möjligheten att förutspå vattenstånd vid större flöden än normalflödet. Detta gjordes genom att i modelleringsprogrammet HEC-RAS skapa två fiktiva tvärsektionsformer, en rektangulär och en triangulär, vars dimensioner anpassades efter ett känt flöde och vattenstånd. Därefter simulerades olika extremflöden för de två olika tvärsektionsformerna vid olika Mannings tal. Resultaten gav att tvärsektionens geometri under vattenytan spelade en obetydlig roll för möjligheten att förutspå vattenstånd vid extremflöden. Studien visade även att tvärsektionens geometri under vattenytan var av mindre betydelse än små variationer i Mannings tal. Om det från framtida studier visas möjligt att generalisera dessa resultat skulle resurserna som idag läggs på att mäta in tvärsektionens geometri under vattenytan istället kunna läggas på att i större utsträckning undersöka andra osäkra parametrar i hydrauliska modeller, som att exempelvis mer noggrant kartera Mannings tal.

  • 60. Stenström, Petter
    et al.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Andersson, Patrick
    Henriksson, Gunnar
    Enlarging the undersized spillway of Höljes dam2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Höljes dam is one of the largest embankment dams in Sweden. Studies have shown that it suffers from several deficiencies that would jeopardize the safety of the dam during extreme floods. The major deficiencies include insufficient spillway discharge capacity in relation to the updated design flood and potential risk of erosion in the dam toe in case of large spillway discharges. To safely pass the higher design flood, four major rehabilitation options are evaluated with the help of hydraulic model tests. Option 1 refers to the use of the existing spillway in combination with extra water storage above the full reservoir retention level (FRRL). Option 2 includes construction of a new, separate tunnel spillway. In Option 3, a new gated spillway, 17 m in width, is added to the right of the existing one. Option 4 refers to construction of a new spillway in the form of a 155 m long overflow weir in the reservoir in combination with moderate storage above the FRRL. In Option 1 and 2, the width of the existing spillway channel remains the same and the stilling basin is enlarged, while in Option 3 and 4, the spillway channel is widened and the stilling basin volume is also increased. This paper addresses the advantages and disadvantages of those options. Together with other investigations, hydraulic model testing provides necessary basis for finalization of each design option in terms of spillway discharge capacity and waterway configuration. After weighing the pros and cons, the dam owner has chosen Option 3 as the final rehabilitation alternative. Further investigations are made to optimize the design.

  • 61. Stenström, Petter
    et al.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Bond, Håkan
    Sjödin, Anders
    Steiner, Rolf
    Increasing the discharge capacity at the Höljes dam in Klarälven, Sweden2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Höljes dam was constructed during 1959-62 and is one of Sweden’s largest embankment dams, with a height of 80 m. The dam is classified in the highest category with regard to dam break consequences. There are three spillways: one bottom outlet, one primary spillway and one log flume. Their discharge capacity at full reservoir level is 185 m3/s, 1290 m3/s and 120 m3/s, respectively. The function of the spillways at full discharge has however been questioned. Two issues are of particular concern: (i) The stilling basin at the end of the chute from the primary spillway was originally designed for a discharge of less than 900 m3/s, and is now in poor condition. One of the concerns is whether the walls of the stilling basin could collapse at high discharge, which could lead to accelerating erosion towards the dam toe. (ii) The discharge from the bottom outlet is conveyed via the old diversion tunnel, in which a hydraulic jump occurs. There is a risk that the diversion tunnel outlet may be inundated at the design flood. The free aeration for the hydraulic jump would then be cutoff, which could lead to large-scale air pulsations and dangerous shock pressures. The design flood has also been questioned and recent recalculations give a 20-30 % increase in the design flood. During 2008, different measures are evaluated for increasing the discharge capacity so as to safely pass a higher design flood. Initially, three alternatives will be analyzed through hydraulic model tests:

  • 62.
    Sundqvist, Per
    et al.
    Vattenfall .
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Analytical solutions of two-dimensional turbulent seepage in rock-fill dams2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Turbulent seepage in porous media, often in rock-fill dams, represents a classical topic. Easy estimation of the seepage flow characteristics facilitates the slope stability analysis of a dam. In this paper, we revisit the analytical approach in two dimensions for solving turbulent seeping flow in homogenous isotropic rock-fill dams lying on an impervious foundation. The derivation of its analytical solution is simplified. The usefulness of the analytical formulations is improved in a sense that explicit expressions of the seepage point location in the downstream slope and the phreatic surface are worked out. The seeping discharge can be easily computed, although its accuracy relies on a good knowledge of the turbulent permeability of a dam. The analytical approach is useful when an approximate answer is needed.

  • 63.
    Söderberg, Anna
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Dahlström, Philip
    Lunds Tekniska Högskola.
    Turning Smart Water Meter Data Into Useful Information: A case study on rental apartments in Södertälje2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Managing water in urban areas is an ever increasingly complex challenge. Technology enables sustainable urban water management and with integrated smart metering solutions, massive amounts of water consumption data from the end users can be collected. However, the possibility of generating data from the end user holds no value in itself. It is with the use of data analysis the vast amount of the collected data can provide more insightful information creating potential benefits. It is recognized that a deeper understanding of the end user could potentially provide benefits for operational managers as well as for the end users. A single case study of a data set containing high frequency end user water consumption data from rental apartments has been conducted, where the data set was analyzed in order to see what possible information that could be extracted and interpreted based on an exploratory data analysis (EDA). Furthermore, an interview with the operational manager of the buildings under study as well as a literature review have been carried out in order to understand how the gathered data is used today and to which contexts it could be extrapolated to provide potential benefits at a building level.

    The results suggests that the EDA is a powerful method approach when starting out without strong preconception of the data under study and have successfully revealed patterns and a fundamental understanding of the data and its structure. Through analysis, variations over time, water consumption patterns and excessive water users have been identified as well as a leak identification process. Even more challenging than to make meaning of the data is to trigger actions, decisions and measures based on the data analysis. The unveiled information could be applied for an improved operational building management, to empower the customers, for business and campaign opportunities as well as for an integrated decision support system. To summarize, it is concluded that the usage of smart water metering data holds an untapped opportunity to save water, energy as well as money. In the drive towards a more sustainable and smarter city, smart water meter data from end users have the potential to enable smarter building management as well as smarter water services.

  • 64.
    Teng, Penghua
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    CFD MODELLING OF TWO-PHASE FLOWS AT SPILLWAY AERATORS2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Due to the high-speed flow in a chute spillway, cavitation damages often occur. This undesired phenomenon threatens the safety of the structure. For the purpose of eliminating the damages, an aerator is often installed in the spillway. To understand its characteristics, physical model tests are a popular method. To complement the model tests, computation fluid dynamics (CFD) simulations are used to study aerator flows. To represent the two-phase flows, multiphase models should be employed. This thesis examines two of them, namely, the Volume-Of-Fluid model (VOF) and Two-Fluid model.

    Based on the background of the Bergeforsen dam, the aerator flow is modelled by means of the VOF model. The simulated spillway discharge capacity is in accordance with the experimental data. Compared with the results, empirical formulas fail to evaluate the air supply capacity of aerator as it is wider than the conventional width. A hypothetical vent modification is proposed. For the original and proposed layouts, the study illustrates the difference in the air-flow conditions. The results show that a larger vent area is, for a large-width aerator, preferable in the middle of the chute.

    To study the flip bucket-shaped aerators in the Gallejaur dam, physical model tests and prototype observations are conducted. The results lead to contradicting conclusions in terms of jet breakup and air entrainment. A CFD model is, as an option, employed to explain the reason of the discrepancy. The numerical results coincide with the prototype observations. The jet breakup and air entrainment are evaluated from air cavity profiles; the air-pressure drops are small in the cavity. The discrepancy is due to overestimation of the surface-tension effect in the physical model tests.

    Based on the experimental data of an aerator rig at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, the Two-Fluid model is used to predict air concentration distributions in the aerated flow. The model includes relevant forces governing the motion of bubbles and considers the effects of air bubble size. The numerical results are conformable to the experiments in the air cavity zone. Downstream of the cavity, the air concentration near the chute bottom is higher, which is presumably caused by the fact that the interfacial forces in the Two-Fluid model are underestimated.

  • 65.
    Teng, Penghua
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Yang, James
    CFD modeling of two-phase flow of a spillway chute aerator of large width2016Inngår i: Journal of Applied Water Engineering and Research, ISSN 2324-9676, E-ISSN 2324-9676, Vol. 4, nr 2, s. 163-177Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An aerator is frequently used to prevent cavitation damages in high-velocity spillways. To understand its characteristics, one often resorts to physical model tests. To complement physical model tests, computation fluid dynamics simulations are used to determine water-air flow behaviors. With Bergeforsen's 35 m wide aerator, numerical modeling has been performed to evaluate its performance and improve its configuration. The parameters of interest include spillway discharge capacity, air entrainment rate, duct subpressure and air concentration in the aerated flow. The simulated discharge capacity agrees reasonably with experimental data. Due to the larger chute width, empirical formulas do not reasonably predict the air demand. To provide the air required by the aerator, its distribution in the cavity must be guaranteed. We thus looked into the air supply system and the air flux in the cavity to improve the aerator function. Larger vent openings in the middle of the chute are preferable for large-width aerators.

  • 66.
    Teng, Penghua
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    CFD modelling of two-phase flow of a spillway chute aerator of large width2016Inngår i: Journal of Applied Water Engineering and Research, ISSN 2324-9676, E-ISSN 2324-9676Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An aerator is frequently used to prevent cavitation damages in high-velocity spillways. To understand its characteristics, one often resorts to physical model tests. To complement physical model tests, CFD simulations are used to determine water-air flow behaviors. With Bergeforsen’s 35 m wide aerator, numerical modeling has been performed to evaluate its performance and improve its configuration. The parameters of interest include spillway discharge capacity, air entrainment rate, duct subpressure and air concentration in the aerated flow. The simulated discharge capacity agrees reasonably with experimental data. Due to the larger chute width, empirical formulas do not reasonably predict the air demand. To provide the air required by the aerator, its distribution in the cavity must be guaranteed. This is challenging for wide spillways. We thus looked into the air supply system and the air flux in the cavity to improve the aerator function. Larger vent openings in the middle of the chute are preferable for large-width aerators.

  • 67.
    Teng, Penghua
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Flows over flip-bucket aerators, physical and CFD modeling with prototype testsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The paper deals with a unique spillway structure, in which an aerator is incorporated in each flip bucket to aerate the flow jet and avoid sub-pressure in the air cavity below. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. CFD is performed to help seek the reason for the discrepancy. With sealed aerators, the model studies exhibit intact flow jets featuring negative cavity air pressure and oscillations, suggesting the need for jet aeration. Both the field observations and CFD indicate that the jets break up, allowing air to penetrate into the air cavities. The resulting cavity air pressure drops are small. The discrepancy is due to the effect of surface tension in the physical models leading to the formation of the enclosed air cavities with negative air pressure, which together with air entrainment in the tail-water gives rise to the jet oscillations. It is suggested, for similar flow phenomena, that compound modelling be performed so as to make amends for physical model test results. 

  • 68.
    Thanke Wiberg, Joakim
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Local Impacts of Climate Change on Fortum´s Hydropower Production2016Independent thesis Advanced level (degree of Master (Two Years)), 300 hpOppgave
    Abstract [en]

    Background: Climate change and the consequences of global warming is probably one of the greatest issues of our time. Among other concerns, global warming is thought to have a great impact on hydrology worldwide. When the atmosphere warms up, river runoff patterns are altered. Nevertheless these future changes are assumed to increase the hydropower potential in some countries. In the public debate it is often referred to a nine year old investigation claiming an increase of 15-20 % in Swedish energy production from hydropower due to the river runoff increase. On the other hand recent research is hinting that the effect of global warming might be masked by climate variability in the nearest future. This study seeks to investigate whether or not the hydropower-intensive company Fortum will benefit from increased future hydropower potential due to climate change.

    Methods: Using historical data, the impacts of global warming on the future potential power production in different types of hydropower plants are estimated by the statistical approach of probability density functions. Moreover spectral analysis is used to investigate the impacts of climate variability in various Swedish watersheds. The study investigates both the nearest future, represented by the years 2021-2050, and the end of the century, represented by the years 2069-2098.

    Results: The future hydropower production is shown to be strongly dependent on the geographical location of a power plant and of the specific power plant type. Although all Swedish rivers where Fortum operates is given more river runoff in the future, some hydropower plants might  suffer from lower hydropower potential due to increased runoff variability. However all reservoir-type power plants in the study, with ability to store water, are calculated to benefit from increased river runoff. Only the run-of-river type power plants, operating with unregulated river flow, are not yet proven to benefit from a changing climate. When considering both specific river and type of power plant, this study indicates that the hydropower potential in the rivers where Fortum operates is expected to increase with 4-15 % towards the end of the century. The one exception is the unregulated river Västerdalälven where this study indicates a possibility of decreased hydropower potential due to climate change. The results of the spectral analysis indicates that up to 30 % of the coefficient of variation in the  monthly mean runoff data is explained by low-frequent periodic fluctuations due to natural climate variability, linked to somewhat predictable climate indices.

    Conclusion: Natural climate variability is likely to be the dominating factor in the nearest future, at least in regulated rivers. Although there are uncertainties about the future potential power production in the run-of-river type power plants, one cannot deny that most of the Swedish rivers where the major hydropower companies operate are strongly regulated. Adding the fact that river runoff will increase as a consequence of global warming, Fortum is likely to gain from an increased hydropower potential. However, this present study highlights the inaccuracies in using the out-of-date estimation of 15-20 % hydropower-potential increase as a forecast of future potential power production in all Fortum-operated hydropower plants.

  • 69.
    Wang, Jun-Zhi
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE). China University of Geosciences, Beijing, China.
    Jiang, Xiao-Wei
    Wan, Li
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wang, Heng
    Wang, Xu-Sheng
    Li, Hailong
    An analytical study on artesian flow conditions in unconfined-aquifer drainage basins2015Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, nr 10, s. 8658-8667Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although it has been reported that flowing artesian wells could be topographically controlled, there is no quantitative research on artesian flow conditions in unconfined aquifers. In this study, the water table, which has a lower amplitude than the land surface, is damped from the topography and used as the boundary condition to obtain the analytical solution of hydraulic head of a unit basin with a single flow system. The term artesian head is defined to characterize the condition of flowing artesian wells. The zone with positive artesian head is called artesian zone while with negative artesian head is nonartesian zone. The maximum artesian head and the size of artesian zones are found to increase with the damping factor and the anisotropy ratio, and decrease with the ratio of basin width to depth and the depth-decay exponent of hydraulic conductivity. Moreover, the artesian head increases with depth nearby the valley and decreases with depth near by the divide, and the variation rates are influenced by the decay exponent and the anisotropy ratio. Finally, the distribution of flowing artesian wells and the artesian head measurements in different depths of a borehole in a small catchment in the Ordos Plateau, Northwestern China is used to illustrate the theoretical findings. The change in artesian head with depth was used to estimate the anisotropy ratio and the decay exponent. This study opens up a new door to analyze basin-scale groundwater flow.

  • 70. Wu, YH
    et al.
    Sund, M
    Magnusson, F
    Zhang, JX
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Numerical and experimental investigations of closure of an emergency bulkhead gate2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The design of hydraulic gates is crucial for safely operating a hydropower dam. An emergency gate is especially important as it protects structures or turbines situated downstream. In this study, both numerical and experimental investigations were performed of an emergency bulkhead gate closure. The gate has a size of 4.978 m (w) by 6.166 m (h) and a thickness of 0.94 m and is subjected to a water head of 80.8 m and a flow rate of 207 m3/s. In an earlier stage, a 1:18 scale model was constructed. The CFD simulations were then made using the RNG k−ε turbulence model and Volume of Fluid method (VOF). A moving dynamic mesh was adopted to follow the gate movement. The goal was to extract the pressure distribution around the gate, subsequently to obtain the hydrodynamic forces acting on the gate and to analyze the flow pattern. The CFD model was validated against the experimental data. The closing speed of the gate and its bottom edge angle were examined in order to reduce the down-pull force and to avoid undesirable flow phenomena. It was found that to lower the gate speed to 8.1 m/min would have a positive effect. The gate would close slower, with reduced forces and less induced vibrations. To change the gate bottom edge angle from 9° to 20-30°, would considerably reduce gate vibrations.

  • 71.
    Wörman, Anders
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Bottacin-Busolin, A.
    Zmijewski, Nicholas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Riml, Joakim
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Spectral decomposition of regulatory thresholds for climate-driven fluctuations in hydro- and wind power availability2017Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, nr 8, s. 7296-7315Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate-driven fluctuations in the runoff and potential energy of surface water are generally large in comparison to the capacity of hydropower regulation, particularly when hydropower is used to balance the electricity production from covarying renewable energy sources such as wind power. To define the bounds of reservoir storage capacity, we introduce a dedicated reservoir volume that aggregates the storage capacity of several reservoirs to handle runoff from specific watersheds. We show how the storage bounds can be related to a spectrum of the climate-driven modes of variability in water availability and to the covariation between water and wind availability. A regional case study of the entire hydropower system in Sweden indicates that the longest regulation period possible to consider spans from a few days of individual subwatersheds up to several years, with an average limit of a couple of months. Watershed damping of the runoff substantially increases the longest considered regulation period and capacity. The high covariance found between the potential energy of the surface water and wind energy significantly reduces the longest considered regulation period when hydropower is used to balance the fluctuating wind power. Plain Language Summary The availability of renewable energy fluctuates significantly with climate and needs to be regulated to be sufficient at all times. This regulation can be achieved by storing hydropower in water reservoirs, but is complicated by the vast spatial distribution of storage locations, size variations in reservoirs, the covariation of renewable energy, and the range of frequencies that need to be considered in climate variations. This study provides a new method of analysis that can provide estimates of the most effective use of hydropower reservoirs and the limits of their use for regulating renewable energy. Based on data from entire Sweden we show how the storage bounds can be related to a spectrum of the climate-driven modes of variability in water availability and to the covariation between water and wind availability. The high covariance found between the potential energy of the surface water and wind energy significantly reduces the longest considered regulation period when hydropower is used to balance the fluctuating wind power.

  • 72.
    Wörman, Anders
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Bottacin-Busolin, Andrea
    The University of Manchester, Manchester M13 9PL, United Kingdom.
    Zmijewski, Nicholas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Riml, Joakim
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Spectral Decomposition of Regulatory Thresholds for Climate–Driven Fluctuations in Hydro- and Wind Power AvailabilityArtikkel i tidsskrift (Annet vitenskapelig)
  • 73.
    Wörman, Anders
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Lindstrom, G.
    Riml, Joakim
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    The power of runoff2017Inngår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 548, s. 784-793Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although the potential energy of surface water is a small part of Earth's energy budget, this highly variable physical property is a key component in the terrestrial hydrologic cycle empowering geomorphological and hydrological processes throughout the hydrosphere. By downscaling of the daily hydrometeorological data acquired in Sweden over the last half-century this study quantifies the spatial and temporal distribution of the dominating energy components in terrestrial hydrology, including the frictional resistance in surface water and groundwater as well as hydropower. The energy consumed in groundwater circulation was found to be 34.6 TWh/fy or a heat production of approximately 13% of the geothermal heat flux. Significant climate driven, periodic fluctuations in the power of runoff, stream flows and groundwater circulation were revealed that have not previously been documented. We found that the runoff power ranged from 173 to 260 TWh/y even when averaged over the entire surface of Sweden in a five-year moving window. We separated short-term fluctuations in runoff due to precipitation filtered through the watershed from longer-term seasonal and climate driven modes. Strong climate driven correlations between the power of runoff and climate indices, wind and solar intensity were found over periods of 3.6 and 8 years. The high covariance that we found between the potential energy of surface water and wind energy implies significant challenges for the combination of these renewable energy sources.

  • 74.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Accuracy of spillway discharge capacity determination, the past & present of physical hydraulic modeling2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The discharge capacity of most dam spillways has been determined through physical hydraulic model tests prior to construction. In Sweden, the majority of dams were built between 1945 and 1975. When the design-flood guidelines were updated, hydrological investigations have shown that many existing dams have a spillway capacity lower than the revised design flood. This leads to the need of structural rehabilitation for a higher level of dam safety. This has necessitated many dams and spillways being re-tested in the laboratory to examine their discharge capacity and the efficiency of energy dissipation at the new higher design flood. For the same spillway layout, differences exist in the spillway discharge capacity between the previous and present model tests. A total of 17 dam spillways are included, including both surface and bottom spillway types. The new experimental test data has shown that the spillway capacity can be greater than, less than or approximately equal to the capacity determined in previous experiments. For some dams, the deviation can be as large as 8-12%. The test data has been analyzed and the possible reasons for the noted discrepancy have been explored. The primary reasons for the discrepancies are thought to be due to the model construction quality and flow measurement method. In some cases, it is found that the dam was not constructed as originally tested and there are certain, albeit minor, differences in the spillway layout, which affects the discharge.

  • 75.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Stilling basin at Vatnsfell dam, Iceland - problem of water cascade and its solution2005Inngår i: HYDRO 2005, The international journal on hydropower and dams , 2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A converging overflow spillway and a bottom outlet share a stilling basin at the Vatnsfell dam, Iceland. When commissioned in 2001, the stilling basin experienced problems of water cascade onto its right rock slope at the discharge interval 70 – 130 m3/s from the bottom outlet. Beyond this scope, the stilling basin functions satisfactorily as designed. Corresponding to the discharge interval, the opening of the radial gate of the outlet varies between 1.0 – 2.5 m, depending on the reservoir water level. The height of the baffle blocks immediately downstream the gate is 1.5 and 2.0 m. An improper relationship between the flow depth and the block height was considered to account for its occurrence. Hydraulic model studies were made to study the reason and to investigate potential countermeasures. The test results led to the suggestion of cutting two or alternatively four baffle blocks located immediately downstream the outlet. To completely remove any blocks or raise the end sill of the stilling basin was not advisable. According to the recommendation, two baffle blocks adjacent to the right sidewall were cut by a half meter in the prototype. Flow release from the outlet showed that the stilling basin functioned satisfactorily and without cascading up to the full discharge capacity. No other countermeasures were considered necessary.

  • 76.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Underwater tunnel piercing in refurbishment of Akkats power station2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Akkats has suffered a number of incidents that were complicated to repair and led to frequent shutdowns. Its existing unit is to be replaced with two smaller units. Underwater tunnel piercing is needed when one of the units is to be put in operation. The open type of piercing is chosen, in which the tunnel and the gate shaft are pre-filled with water. Hydraulic model studies are made to examine involved hydraulic parameters. The deposit profile of the blasted rock in the stone pit and the upsurge in the gate shaft are strongly affected by the plug thickness and shaft water level. To reduce upsurge height, the reservoir and the shaft should have the same water level. A few countermeasures are discussed for upsurge suppression. The stone pit should be optimized for the countermeasure in question so as to reduce intake head losses and prevent the blasted rock from entering the tunnel.

  • 77.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik. Vattenfall AB, Sverige.
    Andreasson, P.
    Bending the spillway flow for safety upgrades2016Inngår i: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 68, nr 11, s. 36-43Artikkel i tidsskrift (Fagfellevurdert)
  • 78.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Andreasson, Patrik
    LTU.
    Instability of embankment dams due to headward erosion caused by spillway flood discharge2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Discharge of high spillway floods can give rise to serious headward erosion in the dam toe, which endangers the downstream slope stability of an embankment dam. In conjunction with dam rehabilitations, hydraulic model tests are made to identify this type of erosion, examine its extent and provide a basis for cost-effective rebuilding design. Four dams are included, i.e. Porsi, Långbjörn, Halvfari and Höljes. Spillway channels are often surrounded by embankments of earth/rock materials grounded on bed rock. The bed rock forms the lower boundary of erosion. Concrete structures limit the erosion development. However, not all the structures will remain in place during high floods. Driven by the spillway water, flow circulations are formed in the downstream area, as is the case with Porsi, Halvfari and Höljes. The headward erosion is a direct consequence of back flow circulations characterized by relatively high-flow velocity and sometimes strong wave motions. As the erosion develops, the main flow direction in the spillway channel shifts somewhat towards the eroded area. The circulation zone increases, which in turn aggravates the headward erosion. The limiting structures play a role in the toe erosion development. Although certain conditions may indicate a predisposition to headward erosion, the risk does not necessarily exist in all dams. The risk for toe erosion has been identified for Porsi and Halvfari, but not for Långbjörn and Höljes. Despite of serious erosion downstream, relatively calm water with insignificant wave motion are characteristic of the flow pattern at the dam toe of the latter two dams.

  • 79.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Andreasson, Patrik
    Cederström, Malte
    Experiences from modifications of curved spillway channels in dam rebuilding projects2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To safely discharge higher design floods, a number of curved spillway channels need to be modified. The design flood of a dam is often released at higher reservoir level, thus giving rise to higher flow velocity in the channel. The combination of more water and higher velocity results in accentuated non-uniform channel flows. The unfavorably distributed flow into a stilling basin or plunge pool aggravates also the energy dissipation. The curved spillway channels of several existing dams are modified in physical model tests. The adopted countermeasures include heightened sidewalls, prolonged spillway piers, new partition walls, streamlining discontinuities in the waterway, the use of differential bottom elevations in cross section, addition of deflector on sidewalls or a combination of several measures. The project experiences are summarized in this paper, with emphasis on flow patterns at high discharges and countermeasures.

  • 80.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Ascila, R
    Vattenfall.
    Nilsson, CO
    E.ON.
    Adding extra spillway discharge capacity, a few dam refurbishment examples in Sweden2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    As required by the revised dam-safety guidelines, the spillway discharge capacity of a large number of the existing dams must be increased so as to release the higher design floods without jeopardizing the structural safety. The extra capacity required falls usually within the scope of 2030%, but in some cases it can as high as 50%. To modify an existing spillway is often the most inexpensive alternative to increase its capacity. When this is difficult due to practical restraints, a new spillway, placed either separately or adjacent to the existing one, needs to be constructed. This paper illustrates several practical examples of dam rebuilding in Sweden that involve either a new spillway or modifications of an existing one.

  • 81.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Billstein, M
    Cederström, Malte
    Vattenfall AB.
    Viklander, Peter
    Sjödin, Gunnar
    Dam safety and rebuilding – a Swedish engineering perspective2006Inngår i: Proceedings of Hydropower 2006 International Conference, Chinese National Committee on Large Dams , 2006, s. 67-79Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The large-scale development of hydropower in Sweden started immediately after the Second World War and reached its peak during the 1950’s and 1960’s. When the dams were built, there were no prescribed criteria for determination of their design floods, and the discharge capacity of many spillways was underestimated. Dam safety was at that time not a subject of state regulatory surveillance, and there were no national directives governing the dam design, construction and supervision. The responsibility rested with the dam developer. With the updated flood guidelines released 1990, many dams have been found to have up to 50% higher design floods than constructed for. As required by the dam-safety guidelines RIDAS, many existing dams, especially high-hazard ones, have to be rebuilt, an issue that involves large capital investment and takes many years to accomplish. The engineering measures include spillway modification, new spillway gates, raising dam crests and/or impervious cores, new erosion protection upstream embankment dams, reinforcement of dam body and re-shaping and strengthening of waterways including stilling basin enlargement. Quite often several rebuilding measures are combined so as to achieve a technically feasible and economical solution. A few dams are given as example to illustrate the rebuilding as imposed by RIDAS.

  • 82.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik. Vattenfall Research and Development, Sweden .
    Billstein, M.
    Engström, F.
    Strand, R.
    Experimental studies on intake headloss of a blasted lake tap2014Inngår i: IOP Conference Series: Earth and Environmental Science, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In existing reservoirs, construction of an intake is sometimes achieved by so-called lake tapping, a submerged tunnel piercing by blasting out the rock plug at the intake. The blasting process involves phases of rock, water, air and gas released from the explosive charge; the resulting entrance profile often differs from design assumptions. The intake headloss is a factor of concern for power generation. For a vertical intake formed by lake tapping, experiments have been carried out in a 1:30 physical model to examine the effect of entrance shapes on intake headlosses. The purpose is that, if there is potential to reduce the headlosses, the originally blasted intake shape would be modified. In the model, five alternative shapes are evaluated. The test results show that to enlarge the vertical shaft area is the most effective way to reduce the intake headloss; to further blast out a narrow channel upstream does not give much effect. Bearing in mind the risk of free-surface vortex at the intake, the influence of the intake modifications on vortex is also checked.

  • 83.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Cederström, Malte
    Spillway hydraulic issues in rebuilding embankment dams – experiences from Vattenfall’s dam-safety program2009Inngår i: Proceedings New Progress on Roller Compacted Concrete Dams, Chinese National Committee on Large Dams , 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In the light of the revised design floods and higher dam-safety requirements, many dams, owned by Vattenfall, have been rebuilt and many others undergo dam-safety evaluations or an upgrading process. Depending upon the dam in question, hydraulic concerns arising from the dam rebuilding may cover dam-slope erosion close to the spillway, increase of spillway discharge capacity, construction of new spillway or rebuilding of existing spillway, re-shaping spillway channel, enlargement of stilling basin or plunge pool and risk for erosion in the dam toe or in the river channels downstream. In this paper, experiences and hydraulic issues of attention are summarised and discussed in the rebuilding of a number of embankment dams.

  • 84.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Cederström, Malte
    Vattenfall AB.
    Upgrading of Stornorrfors dam for safe release of extreme floods2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Comprehensive dam-safety evaluations of the Stornorrfors dam were made with regard to new Swedish dam-safety guidelines including new design flood. This resulted in classification of the scheme as high hazard and identified inadequacy ofin the need to increase the spillway discharge capacity. To adapt to the Swedish dam-safety guidelines RIDAS, Vattenfall AB intendsand to refurbish the dam to raise its safety level in some other respects. The safety requirements in relation to discharge capacity are to be met by an additional spillway., chosen from three rehabilitation proposals and tThree alternatives have been evaluated in detail. Hydraulic model studies are made to assist in the decision-making. The old reserve spillway opening, sealed at present by a salmon ladder and a concrete wall, will be rebuilt into an gated overflow spillway to accommodate the increased design flood, a decision made by taking into account of a range of technical, environmental, social and economic issues.

  • 85.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Engström, Magnus
    Nilsson, Carl-Oskar
    Hydraulic safety of handling extreme floods of at Edensforsen dam, Sweden2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Edensforsen is a high-hazard dam. Along with other engineering measures, a significant increase in its spillway discharge capacity is needed in order to meet the existing dam-safety criteria. A number of design options are examined in order to achieve cost-effective rebuilding. The options includes (A) the use of the existing spillway in combination with extra storage of water above the legal reservoir level, (B) modifications of the abandoned log flume into a spillway, (C) threshold lowering in the existing sector spillway (D) a new, wider spillway with the log flume removed. Some of the options might be combined. To evaluate the measures, hydraulic model studies are made of discharge capacity, energy dissipation and flow patterns downstream. The final choice of refurbishment depends mainly upon the technical feasibility and economical considerations.

  • 86.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Hellstadius, Karin
    Cederström, Malte
    Vattenfall AB.
    Adapting the spillway for updated design flood at Stenkullafors dam, North Sweden2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    New Swedish design-flood and dam-safety guidelines require a higher level of structural and hydraulic safety of the existing dams in the country. The guidelines initiated a review of each river to find good solutions – combinations of retention of water and increased spillway capacity. To comply with the guidelines, a dam-safety program undergoes in the country to rebuild a large number of dams to improve their safety – for higher design floods and also in many other respects. Technical solutions include dam reinforcement, spillway capacity increase and temporary storage of water in large reservoirs. Stenkullafors has a spillway with two gated overflow openings. Its revised design flood is 40 % higher than its existing spillway capacity. Based on a cost-benefit analysis, modifying one spillway opening to a lower crest was chosen as the main measure to cope with the flow. Through hydraulic model tests, the spillway crest profile was optimized so as to achieve the required capacity on one hand and to minimize the cost of the spillway crest and the new gate on the other. The sill elevation in the right spillway opening was lowered by 4.3 m and a new higher tainter gate was installed. The dam has now been rebuilt to higher safety level. This paper addresses hydraulic model tests and the risk of flood occurrence during the construction time. Also, the construction process and difficulties that were encountered are described. Other engineering measures are strengthening of the dam body, new erosion protection on upstream slope, energy dissipater and channel downstream.

  • 87.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Hellstadius, Karin
    Sweco.
    Cederström, Malte
    Vattenfall.
    Case study of spillway modifications – a means to a higher level of dam safety2008Inngår i: Journal of Geotechnical Engineering, ISSN 0733-9410, Vol. 30, nr 11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New Swedish design-flood and dam-safety guidelines require a higher level of structural and hydraulic safety of the existing dams in the country. The guidelines initiated a review of each river to find good solutions – combinations of retention of water and increased spillway capacity. To comply with the guidelines, a dam-safety program undergoes in the country to rebuild a large number of dams to improve their safety – for higher design floods and also in many other respects. Technical solutions include dam reinforcement, spillway capacity increase and temporary storage of water in large reservoirs. Stenkullafors has a spillway with two gated overflow openings. Its revised design flood is 40 % higher than its existing spillway capacity. Based on a cost-benefit analysis, modifying one spillway opening to a lower crest was chosen as the main measure to cope with the flow. Through hydraulic model tests, the spillway crest profile was optimized so as to achieve the required capacity on one hand and to minimize the cost of the spillway crest and the new gate on the other. The sill elevation in the right spillway opening was lowered by 4.3 m and a new higher tainter gate was installed. The dam has now been rebuilt to higher safety level. This paper addresses hydraulic model tests and the risk of flood occurrence during the construction time. Also, the construction process and difficulties that were encountered are described. Other engineering measures are strengthening of the dam body, new erosion protection on upstream slope, energy dissipater and channel downstream.

  • 88.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Johansson, N
    Cederström, Malte
    Handling reservoir floating debris for safe spillway discharge of extreme floods – laboratory investigations2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Floating debris that obstructs the spillway reduces its discharge capacity and could thus constitute a dam-safety risk in an extreme flood situation. Tests are made in a 1:60 Laxede dam model, with about 130 small trees, whose median length is selected on the basis of the prototype data. Without any countermeasure, the spillway capacity is reduced by up to 27%. To prevent debris clogging, two types of debris racks or visors are devised and examined in the laboratory. The visors are composed of sloping beams placed directly on the spillway or on a semi-circular platform. No matter which type of visor one uses, it stops effectively the floating debris and the spillway openings are kept free from the debris. With the same model trees, the reduction in the spillway discharge capacity is only 2 – 3%. The study illustrates the concept of deploying the visors to stop the floating debris, maintain relatively free spillway flow and a marginal reduction in the discharge capacity.

  • 89.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Kung, C. S.
    Nonlinear stability of differential surge chambers1992Inngår i: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 118, nr 11Artikkel i tidsskrift (Fagfellevurdert)
  • 90.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Kung, C. S,
    Stability of air-cushion surge tanks with throttling1992Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 30, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The throttling orifice is introduced into air-cushion surge chambers to improve stability. The presence of the orifice adds another nonlinear term to the dynamic system, and its effect becomes predominant for oscillations with large displacements. By means of linearization, the type of singularities in the phase plane and their stability criteria in case of small oscillations are identified. The nonlinear analysis by direct numerical integration indicates that the system manifests itself as Hopf bifurcation with the surge-chamber size as its controlling factor. The bifurcation point corresponds to Svee's stability criterion. Before bifurcation, an unstable limit cycle may occur around the equilibrium state of practical interest, and it defines the domain of asymptotic stability. After bifurcation, two limit cycles may occur. Because of the existence of the stable one, the chamber size can be smaller than that specified by the Svee criterion. The orifice has stabilizing effect on surge motions.

  • 91.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Kung, C. S.
    Cederwall, Klas
    Large-amplitude oscillations in closed surge chamber1992Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 30, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The governing equations for surge oscillations in a closed surge chamber yield a second-order nonlinear differential equation for constant power. The surge stability is investigated by the direct method of Liapunov, which introduces the Liapunov function from the energy consideration. The nonlinear terms arising from large surges are included. The resulting stability criterion is demonstrated on a phase plane. For the equilibrium point of practical interest, the stability diagram specifies domains of asymptotic stability as a function of the safety factor of the surge-chamber. The diagram indicates that large-amplitude surges necessitate larger chamber size than that laid down by Svee for damping and the surge stability deteriorates with downward oscillations. By postulating sinusoidal surge motion, the critical chamber area is equal to the product of the critical area in case of small oscillations (Svee's formula) and a factor greater than 1.0. The factor is a function of surge amplitude and air cushion parameters for given turbine head. Stability criteria for open surge tanks can be obtained as special cases of those for closed ones.

  • 92.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Lin, Chang
    Li, YD
    Fu, YH
    Tseng, W
    Visualization and measurement of two-phase flow field around an aerator using PIV and BIV techniques2014Konferansepaper (Fagfellevurdert)
  • 93.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Liu, Ting
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Bottacin Busolin, Andrea
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Lin, Chang
    National Chung Tsing University, Taiwan.
    Effects of intake-entrance profiles on free-surface vortices2014Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 52, nr 4, s. 523-531Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Intake free-surface vortices can cause efficiency losses, flow fluctuations and even structural damages. Experiments were performed to examine the effect of entrance shapes on the critical submergence. Seven entrance shapes were devised and tested, including a square-edged, a bell-mouthed, three symmetrical conical and two conical profiles with eccentricity. The focus of the study was on a range of Froude numbers from 0.25 to 0.65. The square-edged shape appeared to show the highest local head-loss compared to other shapes. Steady counter-clockwise vortices characterize all the intake profiles except in a narrow water tank. The experiments show both discrepancy and similarity between the intake profiles. The critical submergence of the bell-mouthed intake is lower when compared to the square-edged shape. For the other profiles, it is proportional to the Froude number. A closer sidewall may lead to larger critical submergence in the case of weak circulations. The results demonstrate that the intake-entrance profile has an important effect on the critical submergence.

  • 94.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik. R&D Alvkarleby Lab, S-81426 Alvkarleby, Sweden.
    Liu, Ting
    Dai, Wenhong
    Teng, Penghua
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Transient Air-Water Flow and Air Demand following an Opening Outlet Gate2018Inngår i: Modelling and Simulation in Engineering, ISSN 1687-5591, E-ISSN 1687-5605, artikkel-id 3194935Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In Sweden, the dam-safety guidelines call for an overhaul of many existing bottom outlets. During the opening of an outlet gate, understanding the transient air-water flowis essential for its safe operation, especially under submerged tailwater conditions. Three-dimensional CFD simulations are undertaken to examine air-water flow behaviors at both free and submerged outflows. The gate, hoisted by wire ropes and powered by AC, opens at a constant speed. A mesh is adapted to follow the gate movement. At the free outflow, the CFD simulations and model tests agree well in terms of outlet discharge capacity. Larger air vents lead to more air supply; the increment becomes, however, limited if the vent area is larger than 10 m(2). At the submerged outflow, a hydraulic jump builds up in the conduit when the gate reaches approximately 45% of its full opening. The discharge is affected by the tailwater and slightly by the flow with the hydraulic jump. The flow features strong turbulent mixing of air and water, with build-up and break-up of air pockets and collisions of defragmented water bodies. The air demand rate is several times as much as required by steady-state hydraulic jump with free surface.

  • 95.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Liu, Ting
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Lin, Chang
    Kao, MJ
    Characteristics of water flow field around an air bubble attached at top of a downward-inclined pipe2013Inngår i: ISTP 24: Proceedings of the 24th International Symposium on Transport Phenomena, Yamaguchi, Japan, 1-5 November 2013, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Flow visualization techniques and high time-resolved PIV were used to investigate the characteristics of water flow field around a stationary air bubble attached at the top of inner-wall of a fully-developed, downward-inclined pipe. Experiments were carried out in a downward-inclined pipe having a slope of 4o, a constant inner diameter of 9.6 cm, and a length of 260.0 cm. Two settling water chambers with different still water levels were connected to the inlet and outlet of the downward-inclined pipe. A pump having a power of 4 Hp was installed between two chambers and used to drive the flow through the inclined pipe. A tilting, honeycomb-like flow regulator made of many straws was placed in front of the pipe entrance in order to smooth the inlet flow. Titanium dioxide powder being uniformly dispersed in the pipe flow was used as tracer both for flow visualization tests and for PIV measurements. The results not only show that horseshoe vortex and reverse flow generated, respectively, at the upstream and downstream of the air bubble can be easily observed in all test cases; but also depict that the flow bifurcates around the stagnation point located at the leading edge of air bubble and prominent formation of the shear layer starts from the separation point and evolves right beneath the air bubble. Based on the precise determination of the specific length scale bs (indicating the representative thickness of a shear layer with the center position being located at ysc) and the specific velocity scale (u – us2) (showing the velocity deficit between the lower and upper bounds of the shear layer), a similarity profile can be obtained with the form of (u – us2)/(us1 – us2) versus the dimensionless shifted height, (y – ysc)/bs , for the mean streamwise velocity in the shear layer beneath the air bubble.

  • 96.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Liu, Ting
    Lin, Chang
    Lu, CH
    Raikar, RV
    Similarity Profile of Shear Layer in Water Flow Field beneath an Air Pocket at Inner Top-Wall of a Horizontal Pipe2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The characteristics of water flow field around an air pocket stuck to the inner top-wall of a horizontal pipe, with approaching flows having fully developed turbulent boundary layer situation, are investigated experimentally. Flow visualization technique using particle trajectory photography and high-speed particle image velocimetry were employed to explore the water flow field around the air pocket in the plane of symmetry both qualitatively and quantitatively. The Reynolds number Re of the pipe flow (= UD/v, where U and D denote the cross-sectional mean streamwise velocity and pipe diameter being equal to 9.60 cm, respectively, and v is the kinematic viscosity of water) is 17,100. The volume of the air pocket tested varies from 1.0 ml to 10.0 ml. The fully developed boundary layer flow in the pipe is examined at first to assure the water flow field around the air bubble is independent of the streamwise position at which the air pocket adhered to the top-wall of the pipe. Based on the measurement results obtained by high-speed particle image velocimetry, the characteristics of water flow fields around the air pocket are presented using the mean velocity vector fields as well as utilizing the distributions of mean streamwise velocity measured at different streamwise sections. In addition, evolution of the mean streamwise velocity measured beneath the air pocket is demonstrated consequently to highlight the formation of shear layer with a reverse flow region inside and extending to the air-pocket surface. Using the non-linear regression analysis with curve fitting to the measured mean streamwise velocity, the appropriate characteristic velocity and length scales are determined precisely to attain the similarity profiles in the shear layer beneath the air pocket. The proposed characteristic length and velocity scales do provide a promising similarity profile as indicated by the data collapse and regression coefficients.

  • 97.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Persson, Jonas
    Norconsult.
    Moustafa, S
    Fortum.
    Upgrade of Långströmmen dam for higher safety standard2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Långströmmen, a high-hazed facility, is planned for rehabilitation in the light of the existing dam-safety guidelines. The safety evaluations made during the recent years have revealed a number of deficiencies with respect to its spillway discharge capacity, rock erosion downstream, dam spillway stability, status of embankment dams and functions of mechanical and electrical systems. After investigations of a number of rebuilding alternatives, economic and technical considerations have reduced to one option, i.e. construction of a new gated spillway with a stilling basin. Three reservoir levels are considered, which also result in different requirements for the spillway stability and freeboards of the embankment dams. The new 18 m spillway is placed separately, with an 80 m sloping chute followed by a stilling basin. To assist in the rebuilding design, hydraulic model tests have been performed. For the reservoir area, the main issues of concern are flow patterns and head losses from the reservoir to the new spillway. For the existing spillway, attentions are paid to the river bank erosion downstream and energy dissipation. For the new spillway, the model study focuses mainly on its orientation, threshold elevation, discharge capacity and energy dissipation.

  • 98.
    Yang, James
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Stenström, Petter
    Ensuring spillway discharge capacity in case of reservoir floating debris2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Reservoir floating debris can clog up the spillway and constitutes, during extreme floods, a potential danger to dam safety. Efforts must be made to mitigate the reduction in the spillway discharge capacity, especially for dams with only two or three spillway openings, as is often the case in Sweden. In connection with the upgrade of a dam, two countermeasures are examined in hydraulic model studies, i.e. a debris visor and an overflow debris weir. A total of 100 small pine trees with roots are used, with a density varying between 650-1000 m3/s and corresponding prototype lengths varying between 15-25 m. The visor is placed obliquely upstream of the spillway where the water depth is 8-10 m. The visor stops effectively the debris. Trees with low density approach the visor afloat and are intercepted in the surface water. Debris with higher density is dragged down when approaching the visor. As a result, it covers the visor height, leading to a reduction in the flow passage. For the overflow weir, if the weir water depth exceeds certain limit, solitary trees or a few trees knitted together can pass the weir without much difficulty. However, for the weir water depth allowed (less than 3 m), if clogging up along the weir starting from the existing spillway and extending upstream, the debris would get wedged and remain on the weir. As a result, the overflow capacity would be restricted, which limits the use of such a fixed weir as countermeasure against debris.

  • 99. Ye, F.M.
    et al.
    Yang, James
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wang, S. R.
    Turbine governing and surge-tank stability1992Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 30, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stability of water-surface oscillations is investigated for the case of a tailrace surge chamber shared by two or more generating units in a hydroelectric power plant. Two kinds of turbine governing are applied for the condition of small-amplitude surge perturbations. Critical stability conditions for the surge chamber are derived by linearizing the ordinary differential equations describing the lumped system. As compared with the result achieved by previous researchers, the common surge chamber requires smaller horizontal crosssection for surge stability. A combination of the proposed manners of governing can be utilized in certain power plants in order to achieve an economical design of the surge chambers.

  • 100.
    Zhang, Aibin
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    CFD Modeling and Optimization of Primary sedimentation tank2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this project, the flow field characteristics of the simplified 2D rectangular primary sedimentation tank in Syvab wastewater treatment plant were achieved by a transient water-air two phases finite-volume method, applying Volume-Of-Fluid (VOF) model. RNG k-ε turbulence model was also employed to calculate the turbulent kinetic energy and its dissipation rate. The undesired hydraulic phenomenon for solid sedimentation was detected in original tank. To reduce the velocity and turbulence intensity of the influent, two categories of optimization methods were proposed, which are installing the baffle and changing the velocity inlet. The modifying effects of different methods were compared by the velocity profiles and the contours of kinetic energy. It turns out that both ways provide a preferred condition for particle settling. In the end, further research was forecasted and the work direction were given.

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